1. Field of the Invention
The present disclosure relates to lighted signs, and, more particularly to thermal regulation of light emitting diodes in channel signs.
2. Description of the Related Art
Light emitting diodes (LED) are used in the sign industry for the illumination of channel signs. The expected lifespan of the LED systems used in the signs is on the order of 50,000 hours. However, the LED's are sensitive to high ambient temperatures. Exposure to elevated temperatures will reduce the luminous output of an LED and reduce lifespan of the LED to unacceptable levels.
The channel sign may include a cover plus a body that forms side walls and a back. The cover may be placed over the body thereby defining a sign cavity, and one or more LED's are disposed within the sign cavity to provide light. The cover is generally translucent and may be clear or may include one or more colors so that the light generated by the one or more LED's passes through the cover. The walls and or back within the cavity may be metallic and/or colored.
The sign cavity of the channel sign is generally substantially thermally insulated so that heat generated by the LED's disposed therein is retained within the cavity. In outdoor applications, the channel sign including the sign cavity may be heated by the ambient conditions including solar heating. For example, a channel sign with black matte aluminum body and a red acrylic cover was mounted on a dark brick wall and exposed to direct sunlight in Minnesota during July, 2005. The aluminum cavity walls of the sign cavity reached temperatures in excess of 135° C. and air temperatures in the sign cavity exceeded 90° C.
Heat-sinks have been used to manage the temperature of the LED's within the sign cavity. The heat-sink dissipates heat from areas with higher temperature to areas with lower temperature by conduction. The heat sink may conduct heat from the LED to the body of the channel sign for dissipation. However, in some circumstances, instead of transferring heat from the LED to the body of the channel sign, the heat sink may transfer heat from the body to the LED thereby heating the LED.
Air circulation has been used to manage the temperature of the LED's within the sign cavity. This may be achieved by using the air vents and/or fans, and may be effective. However the fan may be bulky and noisy and may result in collection of dust and dirt as well as water within the sign cavity.
Timers have been used to manage the temperature of the LED's within the sign cavity. The timer, for example, is set to turn the LED's off during the daytime to avoid operating the LED's when the channel sign is subject to solar heating and hot daytime temperatures. However, this requires adjustment of the timer throughout the year in order to ensure that the LED's are turned on at night and turned off during the daytime.
Photoresistors and similar light detection devices have been used to manage the temperature of the LED's within the sign cavity by detecting sunlight or daylight conditions generally and dark and/or nighttime conditions. The LED's within the channel sign are switched on or off in response to the conditions detected by the photoresistor. The photoresistor must be kept clean as dirt, water, and suchlike can interfere with the transmission of light to the photoresistor and, hence, the operation of the photoresistor. In addition, inclusion of the photoresistor adds to the cost of the channel sign.
Accordingly, a need exists for apparatus and methods for the thermal regulation of LED's within a channel sign.